1. Field of the Invention
The present invention is related to brakes for machinery. In particular, the present invention is related to drum brakes used on crane cable spools and other hoisting equipment.
2. Description of the Related Art
Braking devices for crane cable spools and other hoisting equipment are well known in the art and are used for preventing the cable spool from unwinding after the cable is stopped in the desired position. However, when loads on the cable exceed certain minimum amounts, the conventional drum brakes on many conventional cranes begin to slip or "creep" and the cable slowly unwinds. Such unwinding or creeping is dangerous and can result in injuries to personnel and equipment. It is an object of the present to increase the braking ability of conventional drum brakes.
Exemplary of the braking devices of the prior art are the following U.S. Patents:
U.S. Pat. No. 4,518,153 discloses a safety mechanism for hoisting drums in a hoist having a motor with a motor shaft, a gear reduction unit, a drum, a safety brake drivingly coupled on an operating element on or close to the drum in which a mechanical out-of-sync detector produces a unidirectional brake-setting output from inputs from the drum and the motor shaft, the unidirectional brake-setting rotational output for setting the brake. In a preferred embodiment, an error correction is made into the detector for obtaining a first unidirectional output during normal operation, and the brake-setting unidirectional rotation is in the opposite direction for setting the brake. One form of detector is a mechanical differential assembly and another form of detector is a set of coaxial shafts that measure differential rotation between the drum and motor input shafts. A unique brake actuator is provided and is easily reset remotely after the brake has been set.
U.S. Pat. No. 4,447,044 discloses clutching and braking control for one or more hydraulically driven crane winch drums each having a hydraulically actuated clutch and a brake. Included is a negative braking mechanism having a brake cylinder of the single-acting, spring-return type for normally holding the brake applied by the force of the spring and releasing the brake on fluid pressure actuation. A mode selector valve selectively delivers hydraulic fluid under pressure from two separate sources to the clutch and the brake cylinder in order to condition the winch for a selected one of winching, brake-locking, and free-fall modes. The mode selector valve causes the negative braking mechanism to release the brake in the free-fall modes. The mode selector valve causes the negative braking mechanism to release the brake in the free-fall mode, so that a positive braking mechanism is also provided to permit the operator to arrest the free fall of the load, or the free running-out of the cable, in an exact position desired.
U.S. Pat. No. 3,994,476 discloses an automatic braking arrangement for a windlass. A hoist is described which includes a windlass for taking up and paying out a line which operates a block and tackle. The windlass is provided with a brake which is arranged to operate automatically to prevent unwanted paying out of the black and tackle line whenever a load is on the block and tackle. The brake operating mechanism includes a load sensing lever arm mounted for limited pivotal movement in response to a load being on the block and tackle, and linkage connecting such lever arm with a brake actuator for transmitting its motion to the actuator. The actuator is adapted to respond to such motion by applying the brake on the windlass to prevent its rotation in response to the force of the load.
U.S. Pat. No. 2,464,245 discloses a control for clamshell buckets including a constantly rotating element, a closing drum, a closing drum clutch to impart the rotation of the rotating element to the closing drum, a closing drum clutch lever to actuate the closing drum clutch, a holding drum, a holding drum clutch to impart the rotation of the rotating element to the closing drum, a closing drum clutch lever to actuate the closing drum clutch, a holding drum, a holding drum clutch to impart the rotation of the rotating element to the holding drum, a holding drum clutch lever to actuate the holding drum clutch, and a one-way interlock operatively connecting the closing drum clutch lever to the holding drum clutch in such manner that moving the closing drum clutch lever to set or release the closing drum clutch will respectively set or release the holding drum clutch lever free to operate the holding clutch without operating the closing clutch.
U.S. Pat. No. 2,261,382 discloses a hoist including a main frame having a plurality of transverse plates spaced with respect to each other, carriers within the main frame having tubular extensions, a drum on each tubular extension, a device for securing each drum to each tubular extension, bearings in one transverse plate for one carrier and for the tubular extension of another carrier, a bearing in another transverse plate for the tubular extension of one carrier, a bearing in still another transverse plate for such other carrier, a rotary drive shaft extending through the tubular extensions and the carriers, and driving connections for transmitting motion from the drive shaft to the carriers.
U.S. Pat. No. 1,976,406 discloses a safety brake for a hoisting drum including a brake device for braking the drum, a lever device for operating the brake device, a safety brake device automatically operated upon the release of the lever device toward normal position, and a device for cushioning the engagement of the safety brake to overcome shock in braking the drum.
U.S. Pat. No. 1,877,408 discloses a brake operating mechanism including, in combination, the operating shaft of a brake mechanism, a stationary housing, a shaft extending completely through the housing and directly rigidly connected with the operating shaft, and a device for stopping movement of the shaft transmitted to it from the operating shaft including a brake shoe for co-operating with the housing, and a toggle connection between the shaft and shoe.
U S. Pat. No. 1,811,686 discloses a direct pulling pipe spinning winch including the combination with a standard draw works of a rotary well drilling outfit having a frame, the frame having two end posts and an intermediate post, a drum, a drum shaft carrying the same and supported on the posts, a line shaft supported on the posts, and a device for driving the line shaft and the drum shaft of a rope drum carried by the line shaft, a device within the drum for operably connecting it to and disconnecting it from the line shaft, a device for operating the connecting and disconnecting device from a point adjacent one of the end posts, a brake for the drum, and a device for operating the brake from a point adjacent the other the end posts.
U.S. Pat. No. 1,488,290 discloses a material handling machine including a drive shaft, drum members rotatably mounted thereon, brake elements carried by the drive shaft and yieldably restraining the drum members from rotation thereon, a device for drivingly connecting the drum members to the drive shaft which is operable by elements movable upon the drive shaft.
U.S. Pat. No. 1,573,491 discloses a double drum hoist including a motor casing and reversible motor, a motor shaft extending from the motor, a gear box at the opposite end of the motor shaft, a central protective housing connecting the motor casing and gear box and having openings for the drum cables, a rotatable center bearing around the motor shaft forming a drum shaft, drums rotatable relatively to the drum shaft, a spiral gear on the drum shaft between the drums, an internally spiralled sleeve on the gear forming a main driver having oppositely facing teeth at its sides, toothed drum drivers on the drums adapted to cooperate alternately with the main driver according to the direction of rotation of the motor, a brake for the drum driver, and gearing operatively connecting the drum shaft to the motor shaft.
U S. Pat. No. 1,264,894 discloses an electrically operated winch, specially applicable as an ash hoist, including an electromotor, a belt pulley driven thereby, a belt, a winch drum driven by the belt from the pulley, a brake device on the winch drum, a belt tension adjusting device, an operating lever, and a rod connecting the belt tension adjusting device to the lever on one side of the fulcrum thereof.
U.S. Pat. No. 888,287 discloses a logging device which includes a pull and a return cable for engaging with the logs, a hold back cable, a device for sustaining the hold back cable at the discharging point for the logs, a winding drum for the hold back cable and a device controlled by the pulling in of the return cable for winding up the hold back cable drum.